A Phosphorus Supported Multisite Coordinating Tris Hydrazone P(S)[N(Me)NCHC₆H₄-o-OH]₃ as an Efficient Ligand for the Assembly of Trinuclear Metal Complexes:  Synthesis, Structure, and Magnetism

A phosphorus supported multisite coordinating ligand P(S)[N(Me)NCHC₆H₄-o-OH]₃ (2) was prepared by the condensation of the phosphorus tris hydrazide P(S)[N(Me)NH₂]₃ (1) with o-hydroxybenzaldehyde. The reaction of 2 with M(OAc)₂·xH₂O (M = Mn, Co, Ni, x = 4; M = Zn, x = 2) afforded neutral trinuclear complexes {P(S)[N(Me)NCHC₆H₄-o-O]₃}₂M₃ [M = Mn (3), Co (4), Ni (5), and Zn (6)]. The X-ray crystal structures of compounds 2−6 have been determined. The structures of 3−6 reveal that the trinculear metal assemblies are nearly linear. The two terminal metal ions in a given assembly have an N₃O₃ ligand environment in a distorted octahedral geometry while the central metal ion has an O₆ ligand environment also in a slightly distorted octahedral geometry. In all the complexes, ligand 2 coordinates to the metal ions through three imino nitrogens and three phenolate oxygens; the latter act as bridging ligands to connect the terminal and central metal ions. The compounds 2−6 also show intermolecular CH···SP contacts in the solid-state which lead to the formation of polymeric supramolecular architectures. The observed magnetic data for the (s = ⁵/₂)₃ L₂(Mn(II))₃ derivative, 3, show an antiferromagnetic nearest- and next-nearest-neighbor exchange (J = −4.0 K and J‘ = −0.15 K; using the spin Hamiltonian Ĥ_HDvV = −2J(Ŝ₁Ŝ₂ + Ŝ₂Ŝ₃) − 2J‘Ŝ₁Ŝ₃). In contrast, the (s = 1)₃ L₂(Ni(II))₃ derivative, 5, displays ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions (J = 4.43 K and J‘ = −0.28 K; Ĥ = Ĥ_HDvV+ Ŝ₁DŜ₁ + Ŝ₂DŜ₂+ Ŝ₃DŜ₃). The magnetic behavior of the L₂(Co(II))₃ derivative, 4, reveals only antiferromagnetic exchange analogous to 3 (J = −4.5, J‘ = −1.4; same Hamiltonian as for 3).